1. Field of the Invention
The present invention relates to a device including a structure which is made of a material requiring a firing process at the time of manufacture and a method for manufacturing the device.
2. Description of the Related Art
Various apparatuses and sensors have been developed to observe the course of a biochemical reaction or to obtain a result of a chemical analysis. As one of the apparatuses and sensors, there is proposed a microdevice which has a fine structure of predetermined fluid channel shape, such as a microchannel, in a substrate. Microdevices of this type have been miniaturized using, e.g., a semiconductor manufacturing method, and the whole analysis process leading to obtainment of desired information can be performed on the microdevices.
Such devices are called micro-total analysis systems (μ-TAS) or labs-on-a-chip. Structures including a fine structure, such as a microchannel, in a substrate are called microfluidic devices.
The microdevices are expected, due to minuteness of the amount of an analyte, to decrease in the amount required of a reagent due to a reduction in the amount of fluid contained in the devices and decrease in reaction time, compared with conventional desktop-size analytical instruments.
In a microdevice in which a heater (resistor) is arranged in a microfluid channel to heat fluid passing through the microfluid channel, since the volume of fluid is small, the temperature of fluid quickly tracks the operation of the heater, and the the temperature of fluid can quickly be raised and lowered. Use of such a microdevice allows a more rapid PCR reaction of DNA.
Since many of microdevices as described above including a microfluid channel are based on a glass substrate, machining of a fine fluid channel can be laborious or difficult. For example, the machining requires micromachining technology, such as machining a glass substrate by etching. For this reason, microdevices are costly to manufacture, which leads to the need for an inexpensive machining method. Under the circumstances, there is devised formation of microdevices without micromachining technology, by employing printing using, e.g., glass paste, or lithography technology (see Japanese Patent Application Laid-Open No. 2003-202678).
If a device, including a structure (first structure) which includes metal layers and a structure (second structure) made of a material (e.g., glass frit or glass paste) requiring a firing process at the time of formation, such as a microfluidic device, is fabricated by glass paste printing, lithography technology, or the like, the entire device is subjected to a high temperature at the time of firing of the second structure. At this time, according to the findings of the present inventors, since the first structure is also brought to a temperature close to the high temperature, materials for the metal layers of the first structure interdiffuse due to heat of the firing, and the electric resistance value of a part of the device may unintentionally vary.
For example, in the case of a microfluid channel, the electric resistance value between a heater (made of, e.g., Pt) constituting a first structure and an extraction electrode (made of, e.g., Au) may vary, and the amount of the variation depends on the connection status (e.g., area and thickness) between the components. Consequently, if the interdiffusion occurs, the variability of the electric resistance value increases. If a heat treatment process is repeated a plurality of times, the status of interdiffusion changes with each iteration, and the variability increases further. It is difficult to control the amount of variation in electric resistance value by a process, which therefore creates a need to correct a driving condition for each of heaters on a device. In order to obtain correction values, the electric resistance values of the heaters need to be individually measured. This is so laborious and it reduces operating efficiency.
There is also available a process of inserting an intermediate layer which inhibits diffusion between two components, as disclosed in Japanese Patent Application Laid-Open No. H09-162513. However, if high-temperature heat treatment, such as firing of glass frit or glass paste, is performed, a material for the intermediate layer may diffuse.
There is further available a process of inserting a layer of an intermetallic compound having a high melting point as an intermediate layer, like the method disclosed in Japanese Patent Application Laid-Open No. H11-186263. The intermetallic compound itself, however, also diffuses at a heat-treatment temperature at which glass frit or glass paste is fired.